1. Field of the Invention
This invention relates to acrylic fibers having superior abrasion resistance and flex fatigue properties. The term "acrylic fiber", when used herein, means a fiber in which the fiber-forming substance is any long chain synthetic polymer composed of at least 35% by weight of acrylonitrile units ##STR1## The term "fiber" includes fibers of extreme or indefinite length (filaments) and fibers of short length (staple). The term "yarn", as used herein, means a strand of fibers and the term "tow" means a larger strand of fibers without definite twist collected in loose rope-like form, usually held together by crimp. Tow is the form which most fiber reaches before being converted (e.g. cut) into staple.
2. Description of the Prior Art
Acrylic fibers have the appearance and feel of wool and therefore, are widely used in socks where wool-like appearance and feel are important. Unfortunately, commercially available acrylic fibers lack the level of flex fatigue and abrasion resistance properties that is required to provide socks having truly significant wear performance properties, for example, socks knitted from commercially available acrylic fibers tend to abrade (develop holes) in the toe and heel regions thereof within a relatively short period of time. This deficiency of acrylic fibers has been long recognized and much effort has been expended on the part of acrylic fiber producers to improve the flex fatigue and abrasion resistance properties of acrylic fibers. One approach that has been taken to correct this deficiency is described in U.S. Pat. No. 3,932,577. This approach relates to the wet spinning of acrylic fibers and consists of adding a small amount of water (1 to 8%) to the spinning solutions used to prepare the fibers. Although this approach provides some improvement in abrasion resistance, there is still room for further improvement.
Accordingly, it is the primary object of the present invention to provide acrylic fibers from which socks having excellent wear performance properties can be made.